This invention relates to lubricants, and, in particular to the synthesis of colloidal suspensions for use as lubricants or lubricant additives.
Lubricants, such as oil and grease, are required in products such as bearings, wherein two contacting surfaces roll and/or slide against each other. Under certain operating conditions relating to loads and high speeds, the two surfaces can interact by metal-to-metal contact. This condition requires additives to the lubricants, known as EP additives, which help protect the functional surfaces. Previously, additives were used which chemically reacted with the surface. The present invention does not chemically react with the surface, but instead bonds to the surface and provides a protective layer or coating to the surface. It contains elemental metal particles which are softer than the bearing surfaces and have the ability to coat the surfaces and fill in surface asperities in the surfaces.
A principle object of this invention is to provide a novel lubricant composition which has the ability to fill in surface asperities and reduce friction by forming a lubricating layer on the contacting surfaces of two components in relative motion to each other (i.e., the rolling elements and raceways for a bearing) thereby extending the life of the components.
Another object is to provide a colloidal suspension for use as a lubricant additive which will protect bearing contact or operating surfaces.
Still another object is to provide methods for making such colloidal suspensions and lubricant compositions.
These and other objects will become apparent to those skilled in the art in light of the following disclosure and accompanying drawings.
The invention, briefly stated, comprises a colloidal suspension which behaves as a lubricant or may be added to a lubricant. The colloidal suspension includes a non-magnetic elemental metal core, preferably of tin, surrounded by a surfactant. The metal colloid is about 0.5 microns to about 3 or 4 microns in diameter. The surfactant preferably comprises an octadecenyl amine, a sarcosinate, or a sulfonate, but many other surfactants well known in the art are suitable.
The colloidal suspension is produced by reducing a metal salt to produce nano-phase metal particles and mixing the reduced nano-phase metal particles with a surfactant. The metal is provided as a metal salt which is dispersed in either an aqueous solution, a hydrocarbon (preferably methanol) solution, or a two phase water/hydrocarbon system to make a metal salt solution. The metal salt solution is mixed with a borohydride solution under an oxygen free atmosphere to reduce the metal. The flask in which the reduction occurs is purged with a noble gas, preferably argon. The borohydride solution includes borohydride, hydroxide, solvent, and water. The surfactant preferably also is added to the borohydride solution. The mixture is heated and stirred. The reduction of the metal salt in the borohydride solution with surfactant produces nano-phase elemental metal particles which are coated with the surfactant to produce the colloidal suspension. The colloidal suspension is collected by separating the reaction products from the liquid. This includes distilling the water from the solution, preferably by azeotropic distillation. This leaves a slurry of the solvent and the colloidal suspension which is filtered to separate the colloids from the solution.